The invention relates to an apparatus for detecting air bubbles formed at the time of pipetting reagents in an apparatus for analyzing liquid specimens automatically, or more particularly to an apparatus for detecting bubbles, formed also in a slender reagent container, by securely detecting bubbles when dispensing reagent in a reagent container by means of a pipet (pipette).
In an automatic analyzer, various reagents are used. The reagent in the reagent container is dispensed by a specific amount from the pipet connected to a measuring device such as a syringe, and is discharged into the reaction container. In the reaction container, the specimen and reagent are mixed, and they react with each other.
Bubbles may be formed in the reagent, and if bubbles are formed in the reagent container, a correct amount of reagent may not be obtained. For example, when the reagent container is turned upside down and agitating to thaw the frozen reagent, or when conveying or transporting of a reagent, bubbles are formed. In the case of a reagent containing a component that easily forms bubbles, the bubbles do not break and remain floating on the liquid surface.
On the other hand, in order to avoid deposit of reagent on the outer wall of the pipet, a pipet having a liquid level detecting function is used. When detecting the liquid level, if bubbles are present, the bubble surface may be mistaken for the liquid surface, and accurate dispensing is not possible.
The Japanese examined Patent Hei. 1-45870, (the Japanese Laid-open Patent Sho. 58-154664) discloses a liquid weighing amount confirmation control device for confirming the liquid sampling amount by the pipet by comparing the liquid level height in the container and lower extent of the pipet. In this device, when the difference of the two is more than .+-.10 to 20%, it is regarded to be clogging.
The Japanese Laid-open Patent Hei. 2-40562 discloses a liquid dispensing device for detecting the liquid surface before and after dispensing and for monitoring improper dispensing. It is also proposed to regard the liquid surface detecting position after dispensing in the previous step as the liquid surface detecting position before dispensing of the succeeding step.
In both the device of 1-45870 and the device of 2-40562, the liquid surface detecting means (or level sensor) is installed near the pipet, but separately from the pipet, and is inserted into the container together with the pipet so as to detect the liquid surface.
Accordingly, such structure cannot be applied in a reagent container. This is a serious problem because the trend toward downsizing is particularly accelerated recently. When the reagent container is not so slender, but if the reaction container is slender, the result is the same, that is, a slender suction part is needed.
Besides, since the liquid surface detecting position and liquid sucking (aspirating) position are different, it is difficult to detect bubbles. This point will be explained with the aid of FIG. 1. When the pipet 40 and liquid surface detecting means 41 descend and there is a bubble 42 just beneath the liquid surface detecting means 41, the liquid surface detecting means 41 detects the bubble 42 as the liquid surface 44, thereby stopping the descending motion of the pipet 40 and liquid surface detecting means 41. Since the pipet 40 does not reach the liquid surface, the reagent cannot be sucked correctly. If, for example, the reagent container diameter is 12 mm and the reagent dispensing amount is 10 .mu.l, the liquid surface moving amount is not more than 0.1 mm, and the difference in such a small movement cannot be detected easily.